* The shell now supports an "eval" command, or "$" for short.
* Runs it in an Otto JavaScript VM.
* Some global variables are available, like `d` is the Doodle object
itself, `log`, `RGBA()` and `Point()`
* The shell supports paging through input history using the arrow keys.
* Added an initial Main Scene
With Labels and Buttons so far.
* Labels are pretty much complete, they wrap a render.Text and have a
Compute() method that returns their Width and Height when rendered
onto an SDL Surface.
* Buttons wrap a Label widget and Compute() its size and takes that into
consideration when rendering itself. Buttons render themselves from
scratch in a "Windows 95" themed way, with configurable colors, border
widths and outline.
